As Miffy said, it does depend a lot upon where you want to eat, but I know that for us (2 adults) we worked out that we spend an average of $60 per day on food while we're in Florida.
That includes all meals and snacks, both in and out of parks and all our trips to Publix for groceries (we typically eat most of our breakfasts in our hotel room - easier to buy cereal, milk, bagels etc. than go out most mornings) and includes taxes and tips.
We also eat at a variety of places from the cheapest fast food and buffets to more expensive restaurants, so this figure should work out well if you're going to vary it similarily.